The Naval Research Laboratory has tested a new optical networking protocol that takes full advantage of all-optical transmission paths.

The Just-in-Time protocol does fast light-path provisioning, rapidly setting up and tearing down optical connections. It grew out of work by researchers at North Carolina State University, MCNC Research and Development Institute of Research Triangle Park, N.C., and NRL's Center for Computational Science.

'JIT is a really efficient use of high-performance optical networks,' said Hank Dardy, chief scientist at the Center for Computational Science. 'It's not just a matter of bandwidth; it's time-bandwidth.'

As bandwidth grows, more and more capacity gets wasted in latency, or delays between devices. Researchers who exchange large terabyte or petabyte data sets try to keep the files in optical form during transmission.

'They want to get the electrical routers out of the patch,' said Dan Stevenson, vice president of MCNC's advanced network research group. 'They want to hook their computers up on a dedicated path.'

But it can take weeks to establish an optical connection over a carrier's network, and minutes with generalized multiprotocol label switching, Dardy said.

That becomes a colossal waste of capacity and money on multi-Gbps networks. JIT can reduce the time for opening paths from days or minutes to less than a second, which makes sharing a single wavelength more practical.

'With all-optical, we can't all own the price of the wavelengths,' Dardy said. 'We're going to have to share a wavelength.'

Difficulty sharing

So far, it hasn't been easy, MCNC's Stevenson said. Scientists have grown adept at multiplexing'squeezing multiple wavelengths into an optical circuit, he said, but wavelength sharing 'is very coarse-grained.'

In demonstrations on NRL's Advanced Technology Demonstration Network, JIT set up and released paths in about 10 milliseconds, or one one-hundredth of a second. Stevenson said the protocol can do the job on the scale of a single microsecond, or one-millionth of a second.

'The 10 milliseconds is the time it takes for the electromechanical switches to reconfigure,' he said. 'We want to get down another three orders of magnitude'a nanosecond.'

All-optical networks are in the early stages of adoption, primarily as test beds, but the problem of efficiently using all-optical bandwidth is not new. Researchers at NRL and the National Security Agency began looking at it in the mid-1990s.

'We always said that optics are not efficiently used,' Dardy said.

With bandwidth up to 160 Gbps projected on networks within the next five years, they did not want to settle for incremental fine-tuning. 'We looked at existing protocols' for signaling and routing, but none were for optical networking, Dardy said, 'so we decided to start with a clean slate.'

MCNC entered the program about two years ago, funded in part by NASA and NSA's advanced R&D activity. Working with MCNC were NCSU professors Paul Franzon, Harry Perros and George Rouskas.

In the first ATDnet tests in November 2002, JIT transmitted uncompressed, high-definition TV signals at 1.5 Gbps. A second demonstration last September set up IP data paths linking systems at NRL, the Defense Department's Laboratory for Telecommunications Sciences and the Defense Intelligence Agency.

A third demonstration, this month, presented HDTV for the Federal Communications Commission.

Path provisioning at the nanosecond level could enable interactive distributed computing with large data sets instead of simple bulk transfers.

'We intend to move JIT into grid networks,' Stevenson said. 'We see the grid as a widely distributed computing system, and optical networks as the backplane.'

For the protocol to advance, however, it must undergo open review. Dardy said he thinks it is ready.

'It's mature enough to undergo scrutiny,' he said. 'We want to release it to the public and take it through the standards process.'